Wide frequency band wireless communication systems such as wide-band multicarrier Orthogonal Frequency Domain Multiple Access (OFDM) or Coded Orthogonal Frequency Domain Multiple Access (COFDM) or wide-band multicarrier spread spectrum systems e.g. Code Division Multiple Access (CDMA) provide larger bandwidths which allow larger amounts of data to be transferred to and from a mobile terminal. However, it is anticipated that within the foreseeable future there will always be too little bandwidth available in cellular mobile radio telecommunications system to meet the demand for Internet access and other data services. Voice communications are traditionally circuit switched to provide a high quality of service but with the disadvantage that resources are tied up for the time of a call. With respect to data transmissions various alternatives have been reviewed in the article entitled “Mobilising the Net”, by Geoff Vincent in the IEE Review, November 1999, pages 241 to 245, published by the Institution of Electrical Engineers, UK. Among these the following are mentioned.
High Speed Circuit-Switched Data (HSCSD) which combines voice channels of a narrow band mobile telephone system such as the European GSM system, for example four voice channels can deliver 57.6 kbit/s. However, the loss of capacity of the system is considerable as four radio channels are occupied for the duration of the transmission.
Enhanced Data for GSM Evolution (EDGE) uses a more sophisticated modulation scheme compared with the original GSM system to increase the data rate to 384 kbit/s and can be used in the existing GSM system. The disadvantage of this system is that it requires a very high quality link to be successful. This limits its use as, for example, to indoor environments, where the channel is more stable and predictable.
Universal Mobile Telecommunications System (UMTS) makes use of additional spectrum compared to existing narrow band mobile telephone systems such as GSM and allows transmission rates of up to 2 Mbit/s. This bandwidth is obtained by absorbing lower bandwidth capacity. Whatever extra bandwidth is provided it is most likely to be used for the expansion of high price/high return on investment mobile telephone services and to accommodate the increased number and density of users and not just for data transmissions.
Terrestrial Trunked Radio (TETRA) is a private mobile radio system which can provide 28.8 kbits/s. This data rate is low for transmitting large amounts of data.
General Packet Radio Service (GPRS) is a variant of the GSM system which allows a variable number of timeslots to be allocated to any user. This is advantageous when the transmissions are bursty and of limited length. However, if, for example, a software program or a large data file is to be downloaded to a mobile terminal the rate of continuous data transmission is either limited as generally for GSM or resources must be combined to provide faster download.
An additional problem can be caused by concentration of data requirements. For example, data may become available at a certain time (e.g. stock market results, football scores, company financial information, a pop concert transmitted live via the internet) and there may be a rush of users to obtain this data. If conventional mobile telephone resources are used to access this data, conventional mobile telephone services may be blocked. For example, emergency services may be severely limited or unavailable which is not in accordance with public policy on the use of mobile phones to increase personal safety.
A so-called “cell broadcast” service is known in GSM in which information services may be broadcast to any users in the cell. The disadvantages of this system are that the amount of data is limited and it is not personalised, i.e. users cannot select specific information and the service takes up spectrum which could be used for normal telephone calls.
U.S. Pat. No. 5,987,381 describes a method of downloading navigation data to a moving vehicle. The service may be requested using a mobile telephone from a remote operator who then downloads the data via a communications system. One possibility is to use the mobile telephone system to download. Another possibility is to use another radio communications system but this is not specified in detail. One disadvantage of this system is that an operator must initiate the data download. It would be preferred to have an automatic system.
One proposal for downloading data is to use the Time Division Duplex (TDD) spectrum available in the planned wide-band communications systems presently being considered for 3-G (third generation) mobile telephone networks (e.g. CDMA 2000, UMTS), see “Wideband CDMA for Third Generation Mobile Communications” Tero Ojanperä, Ramjee Prasad, editors, Artech House Publishers, 1998. TDD may be described as a duplex method of transmission whereby uplink and downlink transmissions are carried over the same radio frequency by using synchronised time slots. Time slots in a physical channel are divided into a transmission and reception part, information on the uplink and downlink are transmitted in an alternating manner. One proposed system is to use an asymmetrical TDD system, i.e. there is much more capacity on the downlink than on the uplink because more timeslots are available for downlink than uplink. A WEB (refers to the World-Wide Web or Internet system using html linked pages) browser system is described which provides 10 times the capacity in the downlink direction. One problem with TDD direct sequence spread spectrum systems is that power control and channel equalisation become much more difficult as the mobile terminal and the base station have to transmit at different times so that accurate power measurements are always delayed by one timeslot. This can be alleviated partially by making the timeslots very short but this makes data transmission more inefficient. Another problem with asymmetrical TDD systems is inter-cell interference or inter-operator interference especially when the degree of asymmetry differs from cell-to-cell or from operator to operator. These problems have resulted in the general belief that the TDD spectrum allocated for 3G systems is best used for indoor environments rather than conventional cellular mobile telephone services.
Summarizing the above it can be stated that there is a growing need to be able to download data to a mobile terminal but present plans to provide such a service generally limit or reduce valuable high quality resources which are needed for more quality sensitive transmissions such as speech communication. Fixed access capacity via wirelines is increasing at a very high rate and the gap between the bandwidth and capacity available for mobile services and for fixed access services is widening continuously. Accordingly, there is a continual need for a better use of available radio spectrum to provide data download services to mobile terminals while not affecting voice communications via mobile telephones adversely.
It is an object of the present invention to provide a cellular mobile radio telecommunications system and a method of operating the same which makes more optimal use of spectrum available than the known systems as well as network components such as radio controllers, base stations and mobile terminals.
It is a further object of the present invention to provide a cellular mobile radio telecommunications system, a method of operating the same which provides a specific service which matches that of wireline networks as well as network components such as radio controllers, base stations and mobile terminals for the system.